MATARESE ET AL.: LARVAL DEVELOPMENT OF PACIFIC TOMCOD 



Snout to second anal fin — Distance along body 

 midline to vertical through origin of anterior- 

 most fin ray of second anal fin. 



Meristic Structures 



Counts of meristic structures were made on 128 

 stained M. proximus larvae and juveniles. Sixty- 

 six specimens (3.1-41.1 mm SL) were cleared and 

 stained with Alizarin Red S (Taylor 1967), and 62 

 larvae (5.1-23.4 mm SL) were stained with Aliza- 

 rin Red and Alcian Blue (Dingerkus and Uhler 

 1977). Both series of stained samples were used to 

 make counts of meristic structures and to deter- 

 mine the onset and sequence of ossification as in- 

 dicated by the uptake of Alizarin Red. Structures, 

 including teeth, were considered ossified even if 

 only slightly stained with Alizarin Red. 



Counts on stained larvae and early juveniles 

 were made of first, second, and third dorsal fin 

 rays, first and second anal fin rays, caudal fin rays, 

 left pectoral and pelvic fin rays, branchiostegal 

 rays, gill rakers, abdominal and caudal vertebrae 

 (including the postural centrum), and neural and 

 haemal spines. Counts were made of premaxillary 

 and dentary teeth on 12 specimens (11.9-41.1 mm 

 SL). 



Counts of meristic structures of juveniles and 

 adults of M. proximus, T. chalcogramma, and G. 

 macrocephalus were made from radiographs. 

 Counts were made of first, second, and third dorsal 

 fin rays, first and second anal fin rays, caudal fin 

 rays, and abdominal and caudal vertebrae (includ- 

 ing the postural centrum). 



IDENTIFICATION OF 

 MICROGADVS PROXIMUS 



development of dorsal and ventral procurrent 

 caudal rays before the development of hypurals. 



Considering the collection locations (coastal 

 Oregon and Washington) and the range of myo- 

 mere counts, the specimens could have been one of 

 only three potential species, M. proximus, T. chal- 

 cogramma, or G. macrocephalus . Meristic charac- 

 ters in the literature (e.g., Svetovidov 1948; Miller 

 and Lea 1972; Hart 1973) are inadequate to sepa- 

 rate all three species. Additional counts obtained 

 in this study, particularly caudal vertebrae and fin 

 rays on the superior hypural (Tables 1,2), enabled 

 positive identification of the series as M. prox- 

 imus. 



DEVELOPMENT OF 

 MICROGADUS PROXIMUS 



Pigment Patterns (Figures 1, 2) 



Pigmentation varies in M. proximus larvae but 

 basic trends persist and are usefiil in distinguish- 

 ing the larvae. The importance of these pigment 

 patterns is stressed by Russell ( 1976) for the entire 

 family Gadidae. He feels many of the early larvae 

 can be identified exclusively by specific pigment 

 patterns. We follow his terminology by referring to 

 the postanal pigment as bars according to their 

 position, anterior and posterior. Russell's use of 

 the term "bar" can be confusing, however, when 

 referring to specific areas within a bar. We define 

 bar as: anterior and posterior pigment area each 

 composed of a dorsal and ventral stripe. Descrip- 

 tions of pigment patterns for M. proximus are 

 based primarily on 49 (2.7-31.0 mm SL) recently 

 preserved ( <2 yr) specimens in which fading was 

 minimal. 



A developmental series of M. proximus speci- 

 mens ranging from late yolk-sac larvae to early 

 juveniles was linked by pigment patterns, myo- 

 mere counts, fin development, and meristic counts 

 in larger specimens. They were identified as 

 gadids based on three criteria: 1 ) Distinctive pig- 

 ment patterns, which in small larvae consist of an 

 anterior and posterior pigment bar, each composed 

 of a dorsal and ventral stripe. With further growth 

 of larvae, these bars diffuse into dorso- and ven- 

 trolateral rows of pigment accompanied by devel- 

 opment of a mediolateral line of melanophores. 2) 

 Relatively high (54-58) myomere counts. 3) Pres- 

 ence of a "pseudocaudal" fin ( Ahlstrom and Counts 

 1955) at about 8.5 mm SL, as indicated by the 



Head Region 



Pigment on the head of the smallest larvae 

 (2.7-3.6 mm SL) is limited to a spot posterior to the 

 pigmented eye and some melanophores on the 

 lower jaw (Figure lA). By 4.0 mm SL, 6 or 7 

 melanophores appear on the nape, 5 or 6 on the 

 lower jaw, and a few internal as well as external 

 melanophores on the forebrain. By 5.0 mm SL, 

 added pigment occurs between the eyes, on both 

 jaws and at the jaw angle, and internally, posterior 

 to the eye (Figure IB). Snout pigment appears at 

 8.0 mm SL (Figure IC), and by 10.0 mm SL, pig- 

 ment is added over the dorsal region of the head 

 (Figure IE). Pigment is added to these areas with 



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